1/[csc A - cotA] - 1/sinA = 1/sinA - 1/[csc A + cot A] get everything in terms of sine and cosine
1/ [(1/sinA - cosA/sinA)] - 1/sinA = 1/sinA - 1/ [(1/sinA + cosA/sinA)] simplify this
sinA/[1 - cosA] - 1/sinA = 1/sinA - sinA/[1 + cosA]
Multiply the first term on the LHS by (1 + cos A) in the the numerator and the denominator. The denominator becomes (1-cos^A) = sin^2A.......the same sort of thing is also done to the last term on the RHS....
sinA[1 + cosA]/sin^2A - 1/sinA = 1/sinA - sinA[1-cosA]/sin^2A
Get common denominators - (sin^2A) - on both sides
sinA[1+cosA]/sin^2A -sinA/sin^2A = sinA/sin^2A - sinA[1 - cosA]/sin^2a
sinA/sin^2a + cosA/sin^A - sinA/sin^2A = sinA/sin^2A - sinA/sin^2A + cosA/sin^2A
cosA/sin^2A = cosA/sin^2A